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Old 9th June 2008, 03:46 PM   #1
Pyre is offline Pyre  Canada
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Question Tube equal to one section of a 12AX7?

Is there a 9 pin tube that is equal or very close to one section of a 12AX7?

Thanks
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Old 9th June 2008, 03:57 PM   #2
SY is offline SY  United States
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Why not just use half the tube?

There's a 7 pin single section equivalent with a 6V heater, the 6AV6.
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Old 9th June 2008, 04:06 PM   #3
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Hi Sy,

Thanks for the info. What I am doing is rebuilding a couple of mono PAM-1 preamps but using the Norman Koren “Spiced” PAS schematic. Each channel uses three 12AX7 half sections. I could use 12AX7’s of course but I was hoping for a lower cost half section equivalent.
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Old 9th June 2008, 04:12 PM   #4
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Old 9th June 2008, 04:14 PM   #5
SY is offline SY  United States
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Lower cost? I think it will be more expensive. You're limited to NOS and need twice as many.

High quality 12AX7s are pretty inexpensive. JJ is under $10 brand new.
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Old 9th June 2008, 04:25 PM   #6
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Yes JJ's cost me about 12 bucks each here plus shipping.

I was hoping that there was something in my stash that was equivalent. When I get home I will check if I have any 6AV6's. I do know that I only have two spare 7 pin sockets.

is there any issue with using both sections of one 12AX7 and half of the second one?
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Old 9th June 2008, 04:30 PM   #7
SY is offline SY  United States
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Nope, no issue, and you might even be able to use that last section to improve the design a bit.

One interesting trick is to only power the heater of one section (i.e., 6V between pin 9 and pin 4 or between pin 9 and pin 5). That prevents the cathode of the unused section from being poisoned, and when the first section wears out, you rewire to use the second section.
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Old 9th June 2008, 04:31 PM   #8
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why not use 3 12AX7s? One on each channoel to provide two triodes per channel, and the third to provide a third triode per channel. Crosstalk should be low, despite the sharing.

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Old 9th June 2008, 04:41 PM   #9
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Quote:
Originally posted by SY

One interesting trick is to only power the heater of one section (i.e., 6V between pin 9 and pin 4 or between pin 9 and pin 5). That prevents the cathode of the unused section from being poisoned, and when the first section wears out, you rewire to use the second section.

Thats a great Idea. I have both 6.3v and 12.6v available so it should not be a problem.
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Old 9th June 2008, 04:42 PM   #10
SY is offline SY  United States
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James, for a PAS mod, that works perfectly well. But he's using the PAMs, which are separate mono.
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